In the field of infrared radiation detection, a type of detector referred to as a Schottky barrier or Schottky diode detector is known. An infrared array utilizing such detectors is described in U.S. Pat. No. 3,902,066 issued to Sven A. Roosild et al on Aug. 26, 1975. Schottky barrier detectors may be composed of a variety of materials such as palladium, platinum or iridium which can be fabricated on a base such as silicon by vacuum deposition and then annealed to form a silicide of various barrier heights depending upon the material. For example, palladium silicide on p-type silicon produces a barrier height of about 0.35 ev, platinum silicide produces a barrier height of about 0.27 ev and iridium silicide, which is disclosed and claimed in a copending application of Daryl L. Smith, Ser. No. 298,567, filed Sept. 2, 1981 produces a barrier height of approximately 0.21 ev. Because of the difference in barrier height, the various Schottky barrier detectors provide different wavelength responses to infrared radiation (3.5 microns for palladium silicide, 4.6 microns for platinum silicide and 5.9 microns for iridium silicide).
In the above-mentioned Roosild patent, the detecting array is composed of a number of Schottky barrier detectors all of the same type so as to provide an image of a heat radiating body located remotely from the detector array.
The present invention is an improvement on the detector array shown by the Roosild patent wherein each unit detector or pixel, rather than being composed of a single Schottky barrier detector type, is composed of two or more Schottky detector barrier detectors of different response characteristics. Utilizing two or more different kinds of Schottky barrier detectors in each individual pixel allows, for example, the separation of various "color" components in the received radiation from the remote object and thus provides the ability for spectral separation useful in target discrimination. With the discrimination provided by using different kinds of Schottky barrier detectors in a single array, the system will be able to differentiate between, for example, tactical targets and decoy targets which typically have different spectral signatures.
In a preferred embodiment of the present invention, a three color system will be shown utilizing palladium silicide, platinum silicide and iridium silicide formed on p-type silicon to provide a three color system. Use of these materials allows the array to be formed by vacuum deposition of the various metal layers on the silicon and annealing the whole unit at the same time since the annealing schedule for each of the described silicides is nearly identical; i.e., about one hour at a temperature of between 300 and 400 degrees centigrade. Therefore, the array may be fabricated simultaneously. Furthermore, the spectral responses of these detectors make the array sensitive to the very desirable infrared "window" between 3 and 5 microns in wavelength. Of course, other detector materials may be found having these desirable characteristics and the use of palladium, platinum and iridium silicides on p-type silicon should be considered only an example of the preferred embodiment.